1. Field of the Invention
This invention relates to an antenna system, and more particularly to a dual-band monopole antenna for the wireless local area network (WLAN) system.
2. Description of the Related Art
With the development of the communication industry in recent years, markets of the WLAN have been gradually growing. In conventional techniques, there have been developed many antennas used in wireless communication devices, such as U.S. Pat. No. 6,166,694 issued to Ying on Dec. 26, 2000 entitled xe2x80x9cPrinted twin spiral dual band antenna,xe2x80x9d which discloses a communication device for the wireless communication system. The communication device includes a printed circuit board, a dielectric substrate adhered on the printed circuit board, and an antenna printed on the dielectric substrate. However, the antenna is printed on the dielectric substrate and then disposed on the printed circuit board by the surface mounted technology, so the cost of the final product is high and, in addition, the antenna occupies quite a large area, which does not meet the demand for reduced volumes of current electronic products.
U.S. Pat. No. 6,008,774 issued to Wu on Dec. 28, 1999 entitled xe2x80x9cPrinted antenna structure for wireless data communication,xe2x80x9d which discloses a printed antenna used for laptop computers in WLAN or other types of small, portable, wireless data communication products including a printed circuit board, a hook-shaped radiating metallic line printed on the top surface of the printed circuit board, a feeding point connected to the hook-shaped radiating metallic line, and a ground plane printed on the bottom surface of the printed circuit board. Compared with the above mentioned patent, this invention is characterized in that the antenna is printed on a peripheral card and directly integrated with the system circuit on the peripheral card. However, the antenna is only used for WLAN operation in the 2.4 GHz band.
Accordingly, many antennas in the wireless communication network card equipped in various types of the current electronic products are only operated in a single frequency band. Therefore, it is expected that, with the growing of the market, the performance and the market competitiveness of the wireless communication network card equipped with the antenna that is operated only in a single frequency band are insufficient. Accordingly, to develop the antenna in the wireless communication network card capable of operating in dual bands is the mainstream trend of related electronic products.
In addition, current electronic products are designed to be light, thin, short and small, so it is expected that the volume of the wireless communication card equipped in all types of electronic products will have the light, thin and clever features and appearances. In this condition, the volume of the antenna equipped in the wireless communication network card will be confined in a specific volume.
Accordingly, there exists a need to provide an antenna capable of easily operating in dual bands and suitable for WLAN operation, and the antenna has the light, thin and small features so as to meet the reduced-volume requirement of current electronic products.
It is a primary object of the present invention to provide a dual-band monopole antenna which can be operated in dual bands and easily tuned to the frequency band required for WLAN operation by means of adjusting the resonant frequencies of the antenna.
It is another object of the present invention to provide a dual-band monopole antenna, wherein the antenna occupies a minimum area and is integrated with the system circuit of the microwave substrate.
In order to achieve the above objects, a dual-band monopole antenna of the present invention comprises a microwave substrate, a first horizontal radiating metallic line, a second horizontal radiating metallic line, a vertical radiating metallic line, a feeding point, and a ground plane. The microwave substrate includes a first surface and a second surface. The first horizontal radiating metallic line is printed on the first surface. The second horizontal radiating metallic line is printed on the first surface. The vertical radiating metallic line is printed on the first surface, wherein the first horizontal radiating metallic line and the second horizontal radiating metallic line respectively intersect the vertical radiating metallic line at different positions. The feeding point is disposed on the vertical radiating metallic line, and the ground plane is printed on the second surface of the microwave substrate.
According to one aspect of the present invention, the middle point of the first horizontal radiating metallic line is connected to one end of the vertical radiating metallic line or the vicinity thereof opposite to the feeding point, the middle point of the second horizontal radiating metallic line is connected to the vertical radiating metallic line at the position different from where the first horizontal radiating metallic line connected to, and two ends (free ends) of the two horizontal radiating metallic lines are extended outwards in opposite direction, whereby the antenna is formed as an stacked double T shape.
According to another aspect of the present invention, the path from the feeding point through the vertical radiating metallic line to one of the free end of the first horizontal radiating metallic line forms a first resonant path of the antenna in operation and determines the first (the lower) operating frequency thereof, and the path from the vertical radiating metallic line to one of the free end of the second horizontal radiating metallic line forms a second resonant path of the antenna in operation and determines the second (the higher) operating frequency thereof.
According to a further aspect of the present invention, the feeding point is connected to a feeding metallic line for signal transmission.
According to a still further aspect of the present invention, the feeding metallic line is printed on the first surface.
According to the present invention, tuning of the above-mentioned two resonant frequencies of the antenna is very easy by means of adjusting the lengths of the first and second horizontal radiating metallic lines, and further tuning the antenna to the frequency band required. In addition, the antenna of the present invention is a planar structure, and therefore it has high integration with the microwave electric circuit. The antenna according to one embodiment of the present invention can be operated in dual bands at 2.4 GHz and 5.2 GHz for WLAN operations, and has a desirable antenna gain in the operating frequency bands.